Samson 3766 - Operation; Tuning the Positioner Mounted Onto the Control Valve

38 EB 8355-1 EN
Operation
5 Operation
5.1 Tuning the positioner
mounted onto the control
valve
Starting point and reference variable
When adjusting the positioner directly at the
control valve, the travel (opening angle) must
be adapted to the reference variable.
With a reference variable, for example 0.2
to1bar,thevalvemustmovethroughitsen-
tiretravelrangefrom0to100%(Fig.12,
left).
For positioners for rotary actuator, an open-
ingangle,forexample0to70°mustbeas-
signed to the reference variable.
The starting point is based on the CLOSED
position of the valve.
Depending on the actuator version ("actua-
tor stem extends" or "actuator stem retracts")
and the operating direction of the positioner
(>> or <>), this starting point can be either
the lower or upper range value (0.2 or
1bar)ofthereferencevariable.
The reference variable range and thus the
upper range value determine the travel of
the valve.
Insplit-rangeoperation(Fig.12,right),the
control valves work with smaller reference
variable ranges. The controller output signal
is used to control two control valves, dividing
it such that the valves move through their en-
tire travel range at half the input signal
rangeeach(e.g.rstvalvesetto0.2to
0.6bar,secondvalvesetto0.6to1bar).To
avoid overlapping, allow for a dead band of
±0.05barasshowninFig.12.
The starting point (zero) is adjusted at the
zero adjuster (6.2); the span, i.e. the upper
range value, is adjusted at the span adjuster
(6.1).
During the adjustment, connect a suitable
pressure adjuster to the signal input and ap-
ply air to the supply air input.
100%
0%
0.2 1 bar0.6
0.2 1 bar
100%
0%
< >< <
<
><
<
Reference variable
Input signal
Dead band
OpenOpen
TravelTravel
ClosedClosed
Valve 2 Valve 1
100%
0%
0,2 1 bar0,6
0,2 1 bar
100%
0%
< >< <
< >< <
Fig.12: Normal or split-range operation